Conference circuits for digital systems are well-known in the art. Essentially such conferences use techniques similar to either the summing technique shown by such U.S. Pat. Nos. 3,761,624 issued Sept. 25, 1973 and 3,796,833 issued Mar. 12, 1974 both to Lewis et al., or to the loudest speaker technique as shown by U.S. Pat. No. 3,699,264 to S. Pitroda et al.
Using the loudest speaker approach, a number of variations and improvements have been developed such as the reference level decay of U.S. Pat. No. 3,958,084 to Nicholas issued May 18, 1976.